Littérature scientifique sur le sujet « Couplage fort vibrationnel »

Comment peut-on influencer la réactivité chimique ? Dans ce travail de thèse, j’ai tâché de répondre à cette question en explorant la frontière entre la chimie et la physique. Dans un premier temps, en tirant avantage du solvant 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) qui permet souvent une réactivité exotique, qui peut être attribuée à ses exceptionnelles propriétés physiques. Ces dernières font de HFIP une véritable matrice supramoléculaire, qui nous a permis le développement d’une nouvelle méthode pour la synthèse d’isochromanes fonctionnalisés. Ce faisant, une généralité et une simplicité opératoire inédites pour la synthèse de ce motif important furent atteintes. Dans un second temps, j’ai exploré la capacité de l’hybridation lumière-matière, accessible grâce au couplage fort vibrationnel (CFV) de modifier la cinétique de certaines réactions chimiques. Ainsi, en plaçant entre deux miroirs différents réactifs, j’ai étudié l’impact du CFV sur la nucléophilicité ainsi que sur la réactivité Diels-Alder
How can we influence chemical reactivity? Throughout this thesis, I attempted to answer this question by exploring the frontier between chemistry and physics.First, I took advantage of solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) which often unlocks exotic reactivity that can be explained by its extraordinary physical properties. These properties make of HFIP a veritable supramolecular matrix, which allowed the development of a new method for the synthesis of densely functionalized isochromans. This method displayed unprecedented generality, simplicity, and practicality on the way to this pharmacologically important motif.Second, I investigated how light-matter hybridization, accessed through Vibrational Strong Coupling (VSC) could alter the kinetics of some chemical reactions. In practice, by placing different reactants between two mirrors, I studied the impact of VSC on nucleophilicity, as well as on Diels-Alder reactivity

Cette thèse porte sur l’optimisation du contrôle des Machines Synchrones à Réluctance Variable (MSRV) et en particulier sur la compensation des phénomènes vibratoires. Elle comprend trois points forts : le développement d’une méthode de minimisation des pulsations de couple et sa validation expérimentale, l’études des facteurs qui peuvent influencer la méthode et l’influence de cette méthode sur les autres performances de la MSRV.Tout d’abord, une méthode de contrôle permettant de compenser les ondulations de couple d’une MSRV existante a été développée. Premièrement, une équation analytique du couple est proposée et analysée afin d’exprimer la relation analytique harmonique entre le couple et les courants d’alimentation. La notion de « fonction de couple » est ensuite introduite. Une stratégie basée sur l’utilisation de cette fonction pour minimiser les ondulations du couple est présentée. Deux méthodes de réduction des ondulations de couple utilisant les différents harmoniques de la fonction de couple sont mises en évidence en. Elles ont été analysées et comparées pour répondre aux différents objectifs. Par la suite, la méthode a été validée par les résultats des simulations pour trois technologies de rotor de MSRV parmi les plus répandues. La méthode est aussi validée par la modélisation analytique et la simulation dynamique à l’aide du logiciel Matlab/Simulink ainsi que par les résultats d’expérimentation avec l’aide du banc d’essai.Ensuite, les facteurs qui peuvent influencer la méthode proposée pour réduire les ondulations de couple et les performances dynamiques ont analysés. Dans un premier temps, une amélioration sensible de l’aptitude au démarrage de la MSRV lorsque la compensation des ondulations de couple est mise en œuvre est mise en évidence. D’autre part la sensibilité de la méthode aux erreurs de mesure de position est évaluée afin de quantifier sa fiabilité dans le cas de l’utilisation d’estimateurs lors du contrôle sans capteur. Enfin, l’influence de la saturation sur la méthode proposée est aussi étudiée à l’aide d’une analyse par éléments finis du comportement magnétique de la MSRV.Finalement, l’influence de la méthode de compensation des ondulations de couple sur d’autres performances de la MSRV est analysée. Les courants optimaux ont plus harmoniques que les courants originaux. Par conséquent, les pertes dans le cuivre, dans le fer et dans les semi-conducteurs de l’onduleur sont modélisées analytiquement, calculées et comparées. Les conclusions montrent que les pertes dans le cuivre sont les plus sensibles à la compensation des harmoniques de couple tandis que les pertes dans le fer et dans l’onduleur sont faiblement affectées. D’autre part, la réduction des ondulations de couple peut changer le comportement vibro-acoustique de la MSRV. La dernière partie est consacrée à l’étude de la relation entre les ondulations de couple et le bruit. Une équation est proposée pour évaluer la variation du bruit produit par la compensation des ondulations de couple. Dans cette partie, les simulations dans Flux 2D sont effectuées pour calculer la variation du bruit. En outre, le logiciel professionnel Manatee réalisant l’analyse des vibrations et de l’acoustique est utilisé dans le but de conforter les résultats obtenus par la modélisation analytique
This thesis aims to study the control and optimization of a synchronous reluctance machine for the purpose of improving the vibrational performance. The main works of the thesis can be classified into three parts: the proposed torque ripple reduction method, the factors which can influence the proposed method and the influence of the proposed method.At first, the torque ripple of synchronous reluctance machine is reduced by a control method. Firstly, a torque equation is proposed in order to present the relationship between torque ripple and the optimal currents. Then a new parameter, torque function, is put forward. Based on the torque function, the torque ripple reduction strategy is presented. Two different torque ripple minimizations are proposed by applying different torque function harmonics. They are analyzed and compared in order to define the optimal method. In order to test the proposed method further, the selected torque ripple minimization approach is applied to three SynRMs. The results of finite element simulations imply that the proposed method is effective to decrease the torque ripples of these three SynRMs. The proposed torque ripple reduction method is verified according to the models built in MATLAB/Simulink and the experiment results respectively.Then the factors which could influence the proposed torque ripple reduction method are analyzed. Firstly, torque function is a function of rotor position, current angle and saturation. Based on the model in Simulink, the influence of different starting position on the performance of the studied SynSR is analyzed. Besides, the estimated position errors produced by senserless control could also affect the toque ripple minimization by changing torque function. At last, the influence of saturation on the proposed torque ripple reduction method is introduced because the amplitudes of the optimal currents are increased.In addition, the influence of torque ripple reduction on the other perfomances of SynRM is analyzed. The optimal currents have more harmonics than the original sinusoidal currents. So three losses (copper losses, iron losses and inverter losses) are modeled, calculated, analyzed and compared. According to the results, the copper losses are the most sensible losses. The iron losses and the inverter losses are a little increased and the increased parts can be neglected. Besides, reducing torque ripple by adding stator currents could influence the vibro-acoustic of the studied SynRM. Thus this section aims to explain the relationship between torque ripple reduction and acoustic noise. An analytical equation is proposed in order to evaluate the variation of noise produced by torque ripple reduction. Simulations in Flux 2D have been performed in order to calculate the variation of noise resulted by torque ripple reduction. At last, the software Manatee which is professional in studying the vibration and noise is applied for the purpose of comparing the results with those of the finite element analysis

A methyl (CH3) group that is attached to a large molecule by a covalent bond adopts a preferred conformation with respect to nearby bonds and exhibits large-amplitude torsional motion. Both the preferred conformations and torsional motions are influenced by the local electronic environment. Additionally, the low-frequency torsional modes may couple to other molecular vibrational modes, providing a mechanism for intramolecular vibrational energy redistribution (IVR).

Rotating blades are subjected to vibrations caused by excitation forces due to a non-homogeneous pressure field of the fluid. Therefore, damping devices like tip shrouds are implemented which reduce the vibrational amplitude and apply additional stiffness and damping to the structure. To predict the resulting vibration response and stresses, a three dimensional contact model has been developed to determine the friction forces. The resulting equations of motion are solved in the frequency domain. The developed method has been implemented in a nonlinear forced response code called DATAR designed for the gas turbine division of Siemens Energy. In this paper, the transfer of common Finite Element models of bladings with shrouds or underplatform dampers to the DATAR code is presented. A mapping procedure based on Finite Element shape functions is used to couple the model with the regular contact grid used in the nonlinear vibration analysis performed with the DATAR code. As a practical example, the vibration behavior of a gas turbine blading with interlocked shrouds is investigated with the developed method.

High power and high capacity turbo-compressor systems frequently sustain acoustically induced vibrations. Higher order acoustic modes generated by turbo-compressors often couple selectively with structural pipe resonances producing significant increase in pipe wall vibration. In some instances, these coincidences generate high local stress levels that fatigue pipe shell or pipe attachments. In order to judge the level of dynamic strain and stress in piping systems, elaborate theories are employed. However, these are frequently not practical and relatively difficult to use in industrial applications, for example, in troubleshooting process. First, the accuracy of predicted results depends on assumed boundary conditions. The boundary conditions for on-site cases are rarely known and always difficult to estimate. Second, strains and stresses are complex and often difficult to determine, since they vary in space and time and may be caused by a multimode frequency excitation. Therefore, the strain and stress can only be predicted in reasonable bounds through laborious sensitivity and error analyses, which add further complexity to the already convoluted mathematical predictions. The correct stress level prediction in a structure, by means of directly measured vibrational velocity levels, is very desirable. Therefore, accurate mapping of the vibrational field is necessary. Since the mapping or evaluating of complex vibrational fields is very tedious and expensive using conventional technology (ample number of strain gauges or accelerometers), an alternative technique has been developed: wide field pulsed holographic interferometry. This method provides three dimensional field images of vibrating structures allowing extraction of the actual vibrational responses (displacement and velocity), and calculation of dynamic strain and stress information. These are described by their gradient, peak and phase values obtained from the holograms documenting vibrational fields. This paper describes empirical verification of the wide field pulsed holographic technology which is used to predict a service life of the complex piping structure subjected to multimode frequency excitation. The experimental work was carried out on a sample thin wall vessel, which was either empty or partially filled with water and excited by the hammer or shaker. Through the conversion of vibrational response levels into strain (and stress level), and verification of the conversion against strain gauge measurement results, the technology is proven as a diagnostic tool. It is concluded that there are many advantages of using holography to evaluate complex vibrational fields. They include: i) ‘instant’ results, ii) non-intrusive nature (i.e. the machinery subject to testing can operate without interruptions), iii) satisfactory accuracy, iv) complete and permanent records, and v) significant savings of time and money due to reducing the analysis effort and implementation of suitable recommendations.

Functionally Graded (FG) materials are recent types of engineering materials Fdeveloped as a solution for applications where a couple of relevant properties of different materials are desired in a single continuous composite structure. In these materials, properties are patterned in a way to insure a gradient and continuous property transition direction-wise. This study is a contribution in the literature among other studies but provides an additional understanding of FG Plate structures vibrational behavior in terms of natural frequencies and modal shapes. For this end, an FG plate is modelized and analyzed using AnsysAPDL. Two boundary conditions (all sides clamped “CCCC” and two parallel sides clamped with two others free “CCFF”) for the same plate element and two power law indices “n” are considered. Results are compared with those in the literature and conclusions are drawn accordingly.

Raman scattering is an attractive probe of surface and interfacial chemistry at metals due to the high degree of molecular specificity inherent in the results. One aspect of Raman scattering that enhances its utility for the study of metal surfaces is the ability to deduce orientational information about molecules at these metal surfaces from the presence of oriented electric fields at these surfaces with which selective vibrational modes can couple. These "surface selection rules" have been both theoretically described and experimentally validated for a variety of metal surfaces. Given the wealth of information available from such studies, potential applications for surface Raman scattering span the range from electrochemical to catalytic systems. Thus, considerable effort has been expended in an attempt to develop Raman scattering for the study of surface and interfacial phenomena. These efforts have largely been focused on overcoming problems attendant to sensitivity and selectivity for the interface in the presence of the bulk environment.

The electron-phonon energy dissipation bottleneck is examined in silicon and carbon nanoscale devices. Monte Carlo simulations of Joule heating are used to investigate the spectrum of phonon emission in bulk and strained silicon. The generated phonon distributions are highly non-uniform in energy and momentum, although they can be approximately grouped into one third acoustic (AC) and two thirds optical phonons (OP) at high electric fields. The phonon dissipation is markedly different in strained silicon at low electric fields, where certain relaxation mechanisms are blocked by scattering selection rules. In very short (∼10 nm) silicon devices, electron and phonon transport is quasi-ballistic, and the heat generation domain is much displaced from the active device region, into the contact electrodes. The electron-phonon bottleneck is more severe in carbon nanotubes, where the optical phonon energy is three times higher than in silicon, and the electron-OP interaction is entirely dominant at high fields. Thus, persistent hot optical phonons are easily generated under Joule heating in single-walled carbon nanotubes suspended between two electrodes, in vacuum. This leads to negative differential conductance at high bias, light emission, and eventual breakdown. Conversely, optical and electrical measurements on such nanotubes can be used to gauge their thermal properties. The hot optical phonon effects appear less pronounced in suspended nanotubes immersed in an ambient gas, suggesting that phonons find relaxation pathways with the vibrational modes of the ambient gas molecules. Finally, hot optical phonons are least pronounced for carbon nanotube devices lying on dielectrics, where the OP modes can couple into the vibrational modes of the substrate. Such measurements and modeling suggest very interesting, non-equilibrium coupling between electrons and phonons in solid-state devices at nanometer length and picoseconds time scales.

Analysis of the dynamics of bilinear systems is critical for a variety of civil, mechanical and aerospace structures that contain gaps or prestress that are caused by cracks, delamination, joints or interfaces amongst components. Recently, a method was developed called bilinear amplitude approximation (BAA) to estimate the response of bilinear systems without gaps or prestress. This method was developed on the idea that the bilinear system can be separated into two time intervals both of which the system behaves as a distinct linear system: (1) the open state and (2) the closed or sliding state. In order to couple the linear vibrational response for each time interval, both geometric and momentum constraints are applied as transition conditions between the states. This paper expands the previous BAA method for the case where there are either gaps or prestress in the system. The new method requires the forcing magnitude to be known so that it can accurately determine when the system transitions between the two states, and the new equilibrium positions for each state for a given forcing magnitude. The new method also finds the bilinear frequency of the system, which cannot be computed using the bilinear frequency approximation (BFA) method previously developed since that method is only accurate for the zero gap and no prestress case. The new BAA and BFA methods are demonstrated on single degree of freedom and three degree of freedom systems for a variety of forcing conditions.

The Arnold Engineering Development Center (AEDC) testing complex includes more than 50 wind tunnels, test cells, arc heaters, and other specialized test facilities. Of these, 27 units have capabilities that are unmatched in the United States, and 14 are unmatched in the world. These unique facilities create equally unique operating environments for instrumentation used for monitoring and control of test conditions. Several high flow-rate, supersonic wind tunnels utilize off-the-shelf angular displacement transducers (ADTs) for monitoring the position of 90° valves (i.e. butterfly valves) used to control the air flow-rate and bulk pressure during testing. Due to the high air flow rates in supply and exhaust ducts, there are significant structural vibrations to which the ADTs are subjected. These ADTs have experienced an unacceptably high rate of failure during testing. In the event of an ADT failure, alternative flow paths may, in some cases, be utilized. If an alternative path cannot be found, however, test operations must be suspended while the faulty sensor is replaced; leading to significant cost and schedule impacts associated with the down-time. This paper discusses an effort to understand the root cause of the ADT failures based on design information, and experience in the field. Several alternative mounting conditions were considered in order to reduce the vibrational loads acting on the ADT. A number of the alternatives consisted of utilizing different shaft couplings to couple the motion of the valve stems and the ADT sensor shaft. Experiments were performed at the University of Alabama’s Applied Controls Laboratory to test the effect of the different enclosures and shaft couplings. Preliminary results indicate that the shaft coupling, in particular, have a direct impact on shaft loads transmitted to the ADT. Test results and conclusions are presented.